1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, a backlight unit of an LCD device and reflective means therein that have an improved light efficiency.
2. Discussion of the Related Art
LCD devices have been actively developed as flat display panels in laptop computers, desktop computers, and large-sized information displays because of their high quality image, lightness, small thickness, compact size, and low power consumption. Most LCDs are passive devices in which images are displayed by controlling an amount of light input from an outside light source. Thus, a separate light source (backlight unit) is generally employed for irradiating an LCD device.
There are two types of backlight units, an edge-light type and a direct type, based on an arrangement of a light source within the unit. An edge-light type backlight unit has a light source installed at a side portion of a light guiding plate for guiding light. Further, the light source includes a lamp for emitting light, a lamp holder inserted at both ends of the lamp for protecting the lamp, and a lamp reflective plate for enclosing an outer circumference of the lamp, such that the reflective plate reflects the light generated from the lamp toward the light guiding plate. The edge-light type backlight units are commonly employed in small-sized LCD devices because their compactness.
However, a direct type backlight unit generally provides a higher luminance than an edge-light type backlight unit and as the trend of large-size LCD devices grows, the applications of the direct type backlight unit increase. The direct type backlight unit includes a light source and a reflective plate positioned opposite to the light source. More specifically, the light source includes a cylindrical fluorescent lamp or a plurality of fluorescent lamps arranged at fixed intervals. The reflective plate is provided to irradiate light emitted from the light source to an LCD panel uniformly. According to the related art, the reflective plate refracts light rays based on the number of light sources and the interval between the light sources (for reference, Japanese Patent Publication Nos. 05-10223 and 05-159609).
However, the backlight unit according to the related art requires high light efficiency and great luminance intensity. Since only polarized rays of P-wave emitted from the light source and S-wave of linearly polarized rays are used for irradiating the LCD device, light efficiency is low. Especially when an inclined angle of the reflective plate is large, there is a decrease in P-wave so that the light efficiency is further deteriorated. Accordingly, the rays irradiated to an LCD device by the backlight unit according to the related art are insufficient and the backlight unit according to the related art has poor light efficiency.